This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Patent Application No. 2000-342034 filed on Nov. 9, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to a brake control device for a vehicle. More specifically, this invention relates to a brake control device for a vehicle having a stroke simulator for simulating the stroke amount of the brake pedal and a pressure controlling mechanism for controlling the hydraulic pressure in the wheel brake cylinder.
A known brake control device disclosed in a Japanese patent application publication published on Mar. 23, 1988 as Toku-Kai-Sho 63(1988)-64858 includes a master cylinder that generates a master cylinder hydraulic pressure in response to a depressing force applied to a brake pedal, a wheel cylinder connected with the master cylinder via a hydraulic conduit, a stroke simulator connected with an end of a branch hydraulic conduit branching from the hydraulic conduit, and a pressure controlling mechanism having a pressure source and connected with a halfway portion of the hydraulic circuit between the branch portion and the wheel cylinder. The pressure controlling mechanism controls the wheel cylinder hydraulic pressure by way of a hydraulic pressure generated by the pressure source, and a solenoid valve is disposed at the branch portion and changes the connecting relationship of the hydraulic conduits so that the master cylinder is connected with the stroke simulator when the pressure controlling mechanism is in the normal condition and the master cylinder is connected with the wheel cylinder when the pressure controlling mechanism is in an abnormal condition. This brake control device with the pressure controlling mechanism controls the wheel cylinder hydraulic pressure by the pressure controlling mechanism when the pressure controlling mechanism is in the normal condition. The brake control device controls the wheel cylinder hydraulic pressure by the master cylinder hydraulic pressure in response to the depressing force of the brake pedal only when the pressure controlling mechanism is in the abnormal condition.
In the above brake control device, the master cylinder is always connected with the stroke simulator when the pressure controlling mechanism is in the normal condition. In such a case, the hydraulic pressure which is equal to the master cylinder hydraulic pressure is always applied to the stroke simulator. Therefore, the stroke simulator must have sufficient strength to bear with the hydraulic pressure corresponding to the maximum depressing force applied by the driver. Consequently, the stroke simulator becomes relatively large and its manufacturing cost is also relatively high.
According to one aspect of the invention, a brake control device for a vehicle includes a master cylinder which generates a master cylinder hydraulic pressure in response to a depressing force applied to a brake pedal, a wheel cylinder connected with the master cylinder via a hydraulic conduit, a stroke simulator connected to an end of a branch hydraulic conduit branching from the hydraulic conduit, a first solenoid valve disposed at an intermediate portion of the hydraulic conduit between the wheel cylinder and a branch portion where the branch hydraulic conduit branches from the hydraulic conduit, with the first solenoid valve alternatively connecting or disconnecting the master cylinder with the wheel cylinder, a second solenoid valve disposed at an intermediate portion of the branch hydraulic conduit and alternatively connecting or disconnecting the master cylinder with the stroke simulator, a pressure controlling mechanism having a pressure source and connected at an intermediate portion of the hydraulic circuit between the first solenoid valve and the wheel cylinder to control hydraulic pressure to the wheel cylinder generated by the pressure source, and a controller which controls the pressure controlling mechanism, the first solenoid valve and the second solenoid valve. The hydraulic pressure in the wheel cylinder is controlled by the master cylinder hydraulic pressure in response to the depressing force applied to the brake pedal in a state that the controller controls the first solenoid valve to be open and the second solenoid valve to be closed when the pressure controlling mechanism is in an abnormal condition. The hydraulic pressure in the wheel cylinder is controlled by the pressure controlling mechanism under the control of the controller in a state in which the controller controls the first solenoid valve to be closed and the second solenoid valve to be open when the pressure controlling mechanism is in a normal condition and the master cylinder hydraulic pressure is lower than a predetermined level. The hydraulic pressure in the wheel cylinder is controlled by the pressure controlling mechanism under the control of the controller in a state in which the controller controls the first solenoid valve to be closed and the second solenoid valve to be closed when the pressure controlling mechanism is in the normal condition and the master cylinder hydraulic pressure is equal to or greater than the predetermined level.
The state in which the pressure controlling mechanism is in the abnormal condition corresponds to the state in which the pressure controlling mechanism cannot or is unable to generate the target wheel cylinder hydraulic pressure ordered or determined by the controller. The state in which the pressure controlling mechanism is in the normal condition corresponds to the state in which the pressure controlling mechanism can or is able to generate the target wheel cylinder hydraulic pressure ordered or determined by the controller.
According to another aspect of the invention, a brake control device for a vehicle includes a master cylinder which generates a master cylinder hydraulic pressure in response to a depressing force applied to a brake pedal, a sensor which senses the master cylinder hydraulic pressure, a wheel cylinder connected with the master cylinder via a hydraulic conduit, a stroke simulator connected to a branch hydraulic conduit branching from the hydraulic conduit, a first solenoid valve disposed in the hydraulic conduit between the wheel cylinder and a point where the branch hydraulic conduit branches from the hydraulic conduit to alternatively permit and prevent communication between the master cylinder and the wheel cylinder, a second solenoid valve disposed in the branch hydraulic conduit to alternatively permit and prevent communication between the master cylinder and the stroke simulator, and a pressure controlling mechanism connected to the hydraulic circuit between the first solenoid valve and the wheel cylinder to produce hydraulic pressure, with the pressure controlling mechanism including a pressure source. A controller is operatively connected to the pressure controlling mechanism, the first solenoid valve and the second solenoid valve to close the first solenoid valve, open the second solenoid valve and operate the pressure controlling mechanism to apply the hydraulic pressure produced by the pressure controlling mechanism to the wheel cylinder when the pressure controlling mechanism is in a normal condition and the master cylinder hydraulic pressure sensed by the sensor is less than a first predetermined pressure level, and to close the first solenoid valve, close the second solenoid valve and operate the pressure controlling mechanism to apply the hydraulic pressure produced by the pressure controlling mechanism to the wheel cylinder when the pressure controlling mechanism is in the normal condition and the master cylinder hydraulic pressure sensed by the sensor is greater than the predetermined level.
According to another aspect of the invention, a method of controlling brake force in a vehicle involves generating a master cylinder hydraulic pressure in response to a depressing force applied to a brake pedal, sensing the master cylinder hydraulic pressure, controlling hydraulic pressure supplied to a wheel cylinder from a pressure controlling mechanism that includes a pressure source, introducing the master cylinder hydraulic pressure into a stroke simulator while hydraulic pressure is supplied to the wheel cylinder from the pressure controlling mechanism when the master cylinder hydraulic pressure is less than a predetermined value and the pressure controlling mechanism is in a normal condition, and preventing the master cylinder hydraulic pressure from being introduced into the stroke simulator while hydraulic pressure is supplied to the wheel cylinder from the pressure controlling mechanism when the master cylinder hydraulic pressure is greater than a predetermined value and the pressure controlling mechanism is in the normal condition.